Japanese Translation of PCT Publication No. 2003-535552 discloses a method of synchronizing a received pulse signal in an impulse radio communication device by tracking synchronization based on a correlation between the reference time and signals that are delayed and advanced with respect to the reference time.
FIG. 18 is a block diagram showing a configuration of a conventional impulse radio communication device. Conventional impulse radio communication device 1000 includes amplifier 1002 for amplifying an RF signal received by antenna 1001, filter 1003 for removing an unwanted signal, analog coding section 1004 for converting a signal to an analog signal, splitters 1005 and 1015 for splitting a signal, a plurality of delay devices 1006, 1007 and 1008 for delaying a signal, multipliers 1009, 1010 and 1011 for multiplying signals, integrators 1012, 1013 and 1014 for time-integrating a signal, reception and synchronization control section 1017 for carrying out synchronization determination and delay control in accordance with a correlation, phase delay section 1018 for delaying a phase of a signal, and main receive wavelet code generator 1016 for modulating a phase delay signal and spreading it by the same spreading code.
In impulse radio communication device 1000, amplifier 1002 amplifies a received RF signal to the amplitude necessary for demodulation, filter 1003 removes an out-of-band unwanted frequency band, and analog coding section 1004 generates an analog code. Next, splitter 1005 splits this analog code signal, and delay devices 1006, 1007 and 1008 output three delayed signals, that is, a signal delayed by time L, a signal delayed by time L+Y, and a signal delayed by time L−Y. Then, multipliers 1009, 1010 and 1011 multiply a reference pulse signal generated in main receive wavelet code generator 1016 by the above-mentioned three delayed signals respectively, and integrators 1012, 1013 and 1014 carries out time-integration corresponding to each symbol.
Furthermore, in conventional impulse radio communication device 1000, reception and synchronization control section 1017 determines synchronization in accordance with the correlation of signals and generates decoded data 1019 while controlling phase delay section 1018 to carry out sliding synchronization. At this time, in the case where section 1017 determines that the signal delayed by time L+Y has a higher correlation than the signal delayed by time L when a received path signal with time L is defined as a reference of the correlation, section 1017 controls phase delay section 1018 so as to delay a tracking period. On the contrary, when section 1017 determines that the signal delayed by time L−Y has a higher correlation, section 1017 controls phase delay section 1018 so as to advance the tracking period. Thus, section 1017 carries out adjustment so that synchronization with a transmission symbol rate is obtained.
Thus, a conventional impulse radio communication device receives a modulated signal code-spread by a CDMA (Code Division Multiple Access) method, compares the correlation between a signal delayed with respect to a received path signal and the reference pulse with the correlation between a signal advanced with respect to a received path signal and the reference pulse, and carries out tracking of synchronization from a signal after dispreading in the CDMA.
The above-mentioned conventional impulse radio communication device determines synchronization by comparing time correlation values in a wavelet form. Therefore, when a plurality of correlation positions exist due to multipath, synchronization circuit holds a wrong a correlation position having low electric power.
Furthermore, a conventional impulse radio communication device determines the establishment of synchronization by the same determination waveform as the time when synchronization is maintained after it is established even when a phase change is large as right after receiving is started. Therefore, it takes a long time to carry out acquisition.